Safe operation of switchgear apparatus in a dangerously explosive production environment, for instance, in coal and ore mines, at enterprises of the mining-and-chemical industry, and petroleum and gas industries, is of prime importance.
The explosion protection of such switchgear apparatus is provided by an explosion-proof enclosure which is capable of withstanding the pressure of an explosion and preventing propagation of the explosion products into the surrounding atmosphere.
In prior art apparatus, the control, protection and switching electric devices are arranged on a removable panel mounted on special brackets in the explosion-proof enclosure; some of the devices are arranged on the panel face, and the rest of these, on the panel back.
However, practice has demonstrated that such an arrangement of the electric devices is inconvenient for various repair and preventive jobs whose accomplishment is hampered by a limited space within the enclosure. Moreover, inspecting the devices arranged on the panel back requires a complete dismounting of the panel, i.e. its removal from the brackets.
There is also known an explosion-proof switchgear (USSR Inventor's Certificate No. 212,351) which comprises an enclosure housing a carriage mounted on a guide and coupled by a pivot pin to a chassis. The enclosure is divided by a partition into two compartments, one of which houses the fixed part of a separable contact system, and the other, the chassis. The chassis carries electric devices, such as a contactor, control and protection units, and the movable part of the separable contact system. The contactor is mounted on the chassis side whereon the movable part of the separable contact system is arranged, and the control and protection units, are arranged on the reverse side of the chassis. The guide carrying the carriage is secured to the internal side wall of the enclosure.
The chassis is movable horizontally along the guides through the use of the carriage and pivotable around the pivot pin. In the working position, the chassis is inside the enclosure, providing for an electrical contact between the parts of the separable contact system. This affords free access only to those devices which are arranged on the chassis face, i.e. on the reverse side with respect to that whereon the movable part of the separable contact system is accommodated.
To gain access to the contactor for various repair and preventive jobs, the chassis has to be pulled out of the enclosure and rotated around the pivot pin, which requires an additional working space and is thus undesirable under limited space conditions, such as in mine workings.
Besides, the arrangement of the guides on a side wall inside the enclosure may over a period of time cause a misalignment of the separable contact system contacts and hence a deterioration of the electric contact therebetween.
Another disadvantage is that, because of an angular deflection of the contacts and the thermal deformation of the chassis, the construction of the above apparatus is incapable of ensuring adequate reliability of the electric contact.